The present invention relates to apparatus for the flow control of the flue gas to combustion air ratio in a reversible regenerative heating system of the type having a pair of regenerators, a first line for supplying air to one of the regenerators, a second line for removing flue gas from the regenerators and valves respectively for controlling the flow rate of air in the first line and the flow rate of the flue gas in the second line.
Regenerative systems of the above type are increasingly used to provide heating of a charge held in an enclosure such as a furnace. While one regenerator supplies combusted fuel e.g. natural gas to the furnace the other serves as a flue to remove the spent gas from the furnace as waste gas to atmosphere. After a predetermined period the regenerators reverse roles and that regenerator previously supplying combusted fuel gas now serves as a flue for waste gas while the other regenerator now provides the combusted fuel gas. The waste gas is used to heat up a heat storage bed with which each regenerator is provided. The heat retained in the bed is then subsequently released to preheat combustion air which passes through the bed for preheating to serve as the support for combustion of the fuel gas within the burner of the regenerator.
The regenerators are connected to a reversing valve which is itself connected to a flue gas exhaust duct and a combustion air inlet. The reversing valve is operable to connect one regenerator to the exhaust duct when that regenerator is serving as a flue and the other regenerator to the combustion air inlet when this is supplying combusted fuel. Periodically the reversing valve reverses these connections.
The flow rates of flue gas along the exhaust duct and of the combustion air along the inlet are controlled by valves and it is important that in use the mass flow rates of flue gas and air are balanced to maximise system efficiency.
In order to achieve this balance wherein the ratio of the flow rates of flue gas to combustion air are maintained constant it is conventional to adjust the setting of the flue gas valve in accordance with the varying gas pressure within the furnace chamber. However, if the chamber is "leaky", that is flue gas escapes from the chamber before entering the regenerator which is in its fluing mode, then the flue gas flow rate can vary appreciably without the chamber pressure varying significantly. This will lead to a variation in the flow ratio of the flue gas to combustion air and an out of balance situation.